Voice messaging systems (VMS) have proliferated in both residential and business use. In the residential context, a VMS can be as simple as an answering machine. In the business context, a VMS can be as complex as a multi-million dollar system for use in telephone switching centers. It is in the business context with which the present invention is concerned. With the proliferation of VMSs, voice messaging service providers have required higher and higher processing capacity out of their VMSs. For example, the ability to handle large number of calls simultaneously is important where the subscriber base to a single VMS is large. In addition, the capability of storing large amounts of voice messages efficiently is an important consideration. Although some VMS manufacturers have taken the approach of simply increasing the number of input/output telephone ports in their VMSs or simply increasing the number of storage devices in each VMS, the physical constraints of such an arrangement often are impractical.
In addition, VMSs have expanded beyond their traditional role of merely being a reservoir of voice messages. Indeed, many modem VMSs include the ability to connect a calling party to the subscriber. Thus, the voice storage function of a VMS is an ancillary function to the more primary function of connecting a calling party (referred to also as the caller) to a subscriber (referred to also as the called party). This feature is also referred to as a "meet-me" feature. For example, one such system that connects a calling party to a called party is described in U.S. Pat. No. 5,307,399 to Dai et al. and assigned to the same assignee of the herein invention. In addition, a commonly assigned co-pending application Ser. No. 08/302,682, herein incorporated by reference, describes in detail a method of connecting a calling party to a called party. However, as described in the '399 patent and '682 pending application, when a calling party and a subscriber are ultimately connected and in conversation, one incoming port (referred to also as a trunk line) of the VMS and one outgoing port of the VMS are occupied. The number of conversations is thus limited to the number of incoming and outgoing ports of the VMS. Typically, the number of ports in a VMS is on the order of 100 ports. Therefore, the maximum number of meet-me connections would be fifty and, in that case, any additional calls to the VMS would encounter a busy signal.
To expand the capacity of VMSs to provide these services to a large number of subscribers in an efficient manner, it is necessary to provide a new system architecture in order to provide adequate service.